We're told that some retailers are seeing “ETL” (End of the line) warnings on ordering systems in various parts of the world. In a few places, the estimated arrival time of new Canon EOS 5D Mark III retailer orders has gone from 2 to 5 days and at least one retailer has seen “unknown” for arrival time. Stock levels for the camera have been fine for years, so this change is noticeable.
These sorts of things generally start happening a couple of months ahead of a replacement product announcement, as one of the same sources has said this happened recently with the EOS-1D X, as they started seeing stock availability changes in December.
The time frame in this case puts an announcement coming after NAB 2016 which runs from April 16 – April 21.